This invention relates to a multi-element zoom lens whose focal length is varied in response to a desired magnification change by varying the pressure of a gas enclosed between at least two of the lens elements and, more particularly, to an improved mechanism for varying the pressure simultaneously with lens movement.
As is known in the art, multi-element zoom lenses typically achieve a variation in focal length by mechanically varying the spacing between elements or groups of elements. U.S. Pat. Nos. 3,630,599 and 3,640,605 are representative of such lenses. These lenses require very precise movement of lens elements or lens groupings typically involving use of cams and related linkages. These demands result in relatively high cost.
A technique for varying focal length in a compound lens by varying gas pressure at the interlens media has been described by James D. Rees in an abstract entitled "Technique for Varying Focal Length of a Lens" published in Xerox Disclosure Journal, Vol. 1, No. 11/12, November/December 1976. U.S. Pat. No. 4,331,388 discloses a preferred lens construction using a preferred group of gases in an enclosed cavity between lens elements.
It is desirable, for gas zoom lens configurations, to vary the gas pressure by a simple, inexpensive mechanism. The present invention discloses a piston/cylinder controlled gas pressure system which correlates gas pressure changes with movements of the lens through magnification changes. More particularly, the invention relates to a gas zoom lens assembly for projecting an image of an object on an object plane onto an image plane at various magnifications comprising, in combination, a group of opposed, symmetrical lens elements defining at least a central cavity therebetween, said central cavity filled with a gas having a characteristic index of refraction, means for moving the lens towards and away from the image plane in response to magnification selections and means linked to said lens movement means to simultaneously vary the pressure of the gas within said cavity so as to change the focal length of the gas in response to changes in magnification ratio.